1. Field of the Invention
The present invention concerns vibration motors.
Vibration motors are also known as ultrasound motors, referring to their preferred frequency of operation, or piezo-active motors, referring to their preferred excitation material.
2. Description of the Prior Art
FIGS. 1 and 2 schematically illustrate the operating principle of one example of a vibration motor.
The motor shown in the above figures has a rotor disk 1 mounted on a frame 2 to rotate about a shaft 3.
It also includes a stator 4 that drives rotation of the rotor 1 by a combination of cyclic tangential deformation of its surface in contact with the rotor and a synchronous perpendicular force.
In the example shown in FIGS. 1 and 2 the stator include two plates 4a, 4b disposed one on each side of the rotor disk 1. Each of the two plates 4a, 4b comprises a plurality of regularly distributed contact sectors 5 with active members 6 between them which cause said contact sectors 5 to move away from each other or towards each other cyclically. The active members 6 are piezo-electric, magnetostrictive or electrostrictive members, for example.
The contact sectors 5 of the two plates 4a, 4b are exactly superposed. The facing contact sectors 5 of the two plates 4a, 4b are connected by active members 7 disposed between said plates. The active members 7 are deformed cyclically so that said contact sectors 5 successively grip and then release the disk of the rotor 1.
The combination of the tangential deformation created by the active member 6 and the normal force created by the active members 7 generates by friction a non-null average force driving continuous rotation of the rotor.
Vibration motors have many advantages.
In particular, they have a high torque at low rotation speeds. As a result no or little reduction gearing is required in many applications, unlike conventional electric motors.
Also, vibration motors often have a much higher power per unit mass than conventional gear motors (approximately 3 times greater).
However, the mechanical power ratings of vibration motors are limited to a few tens of watts.
One aim of the invention is to propose a vibration motor structure capable of producing much more power than existing vibration motors whilst retaining the advantages of the light weight of vibration motors, even at high power, and without significantly increasing their overall size.